Process for hydroelectrolytically dimerizing acrylonitrile

ABSTRACT

IN THE PROCESS FOR ELECTRICALLY HYDRODIMERIZING ACRYLONITRILE, THE IMPROVEMENT WHICH COMPRISES SEPARATING AN ELECTROLYTE EFFLUENT CONTAINING AN ELECTROLYTIC SUPPORTING SALT, ACRYLONITRILE, ADIPONITRILE AND ELECTRODE REACTION-IMPAIRING MATERIALS INTO OILY AND AQUEOUS LAYERS, REMOVING THE ELECTRODE REACTION-IMPAIRING MATERIALS CONTAINED IN THE OILY LAYER AND RECYCLING THE RESULTING OILY PHASE THUS PURIFIED TO THE ELECTROLYTE.

Aug. 8; 1972 I om SEKQ ETAL 3,682,792

PROCESS FOR HYDROELECTROLYTICALLY DIMERIZING ACRYLONITRILE Filed April21, 1971 I s sheets-shut 1 INVENTORS Maomi. Seko, Akira Yomiyama,Shinsaku Ogawa, Tetsuya Miyake, Ryozo Komori and Norito Ogawa BY WATTORNEYS Aug. 8, 1972 PROCESS FOR HYDROELECTROLYTICALLY DIMERIZINGACRYLONITRILE Filed April 21, 1971 MAOMI SEKO A 3 Sheets-Sheet 2 FIG. 2

REFINING STEP INVENTORS Maomi Seko Akita Yomiyama, Shinsaku Ogawa,Tetsuya Miyake, Ryozo Komori and"Norito Ogawa BY )i Aug. 8, 1972 o 'sETAL 3,682,792

PROCESS FOR HYDROELECTROLYTICALLY DIMERIZING ACRYLONITRILE Filed April21, 1971 3 Sheets-Shoot 3 FIG. 4-

INVENTORS Maomi. Seko, Akira Yomiyama, Shinsaku Ogawa, Tetsuya Miyake,Ryozo Komori and Norito Ogawa ATTORNEYS United States Patent Int. Cl.C07b 29/06; C07c 121/26 US. Cl. 204-73 A 13 Claims ABSTRACT OF THEDISCLOSURE In the process for electrically hydrodimerizingacrylonitrile, the improvement which comprises separating an electrolyteeflluent containing an electrolytic supporting salt, acrylonitrile,adiponitrile and electrode reaction-impairing materials into oily andaqueous layers, removing the electrode reaction-impairing materialscontained in the oily layer and recycling the resulting oily phase thuspurified to the electrolyte.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to a process for electrolytically hydrodimerizing acrylonitrile(called AN hereinbelow) wherein the electrolyte is separated into oilyand aqueous layers, electrode reaction-impairing materials are removedfrom the oily layer and the resulting purified oily layer thus purifiedis recycled to the electrolyte while conducting the electrolysis.

(2) Description of the prior art A number of processes have heretoforebeen known of hydrodimerization of AN. 'For example, the electrolysisusing a homogeneous solution as the electrolyte is disclosed in US.Pats. 3,193,477, 3,193,480 and 3,193,481 and use of an emulsion as theelectrolyte is disclosed in Belgian Pats. 699,926 and 699,928. Anotherprocess is described in Belgian Pat. 684,436. Methods for the recoveryof adiponitrile (called ADN hereinbelow) from the electrolyte resultedfrom these electrolytic processes are known in UJS. Pat. 3,267,131 usinga homogeneous solution as the electrolyte and Belgian Pat. 706,573 usingan emulsion as the electrolyte.

However, these processes are disadvantageous in that the electrolysis,when carried out over a long period of time, is associated withgradually increasing formation of by-products particularly ofpropionitrile (called PN hereinbelow) to reduce the yield of ADN on thebasis of AN consumed. It is also disadvantageous in these processes thatpolyacrylonitrile or degenerated products thereof tend to deposit uponthe surface of the cathode. In order to overcome these disadvantagesmethods such as those described in UJS. Pat. 3,335,162, Belgian Pat.981,980, Netherlands Pat, 651,550 and Belgian Pat. 716,095 have beendevised. For example, an attempt is made in US. Pat. 3,335,156 ofremoval of the electrode reaction-impairing materials by removingdeposits of partially hydrolyzed polyacrylonitn'le formed in theinterface after the catholyte is allowed to stand for separation.However, even with these attempts, tendencies for the by-products to begradually accumulated during the production of ADN for a sufficientlylong period of time to reduce the yield of ADN as well as for thepolymers to be attached are hardly avoidable.

Even if a catholyte is prepared prior to the electrolysis 3,682,792Patented Aug. 8, 1972 ice from freshly purified AN, electrolyticsupporting salt and other additives used for the electrolysis while theelectrode reaction-impairing materials are removed, it is difii cult tomaintain the yield of ADN higher than 90% on the basis of AN consumedduring the electrolysis conducted for a long period of time, forexample, over more than 400 hours. This is especially remarkable withthe process operated on an industrial scale wherein every long termoperation is not accompanied by the adjustment of the catholyte but justby the removal of the agglutinates on the surface of the cathode. Undersuch circumstances, maintenance of the yield of over 400 hoursnecessarily becomes difficult even if the yield of ADN from to isachieved in the initial 400 hours. The fact, which is supported, forexample, by the experiment described hereinbelow in comparative Example2, implies that reduction in the yield of ADN is caused not only byagglutinate degenerated polyacrylonitrile upon the surface of thecathode but also by electrode reactionimpairing materials increasinglyaccumulated in the electrolyte.

SUMMARY OF THE INVENTION It is an object of this invention to provide amethod of preventing by-production of RN promoted by electrodereaction-impairing materials and reduction in the ratio of forming ADNwith passage of time during a long operation by successively eliminatingthe electrode reaction-impairing materials accumulated in theelectrolyte from the system through purification of the oily layerseparated from the electrolyte. Another object is to provide a method ofsuccessively eliminating electrode reaction-impairing materials from thesystem by purifying the oily layer separated from the electrolyte whileextracting the electrode reaction-impairing materials in the aqueouslayer separated from the electrolyte by adding additional ADN thereto,followed by recycling the resulting purified aqueous layer to thecathode, thereby preventing byproduction of PN promoted by the electrodereactionimpairing materials and reduction in the yield of ADN during along operation. Other objects will 'be apparent from the descriptionshereinbelow.

We have found that the rate of by-production of PN can be remarkablyreduced and the yield of ADN increased, as well as the agglutinates onthe surface of the cathode can be substantially reduced to a negligibledegree thereby enabling stable electrolysis for a long period of time byseparating the electrolyte into oily and aqueous layers and successivelyeliminating the electrode reactionimpairing materials contained in theoily layer out of the system by means of adsorption on a cation exchangeresin, extraction with an aqueous acid solution, or extraction from thecatholyte by addition of ADN. This invention is based upon the abovefindings. According to a more preferable embodiment of the invention,while conducting purification of the oily layer in such a method as setforth above, the purification of the aqueous phase is also carried outby adding ADN to the aqueous layer to transfer the electrodereaction-impairing materials contained in the aqueous layer into theoily layer comprising ADN, the remaining aqueous layer is recycled tothe catholyte and said oily layer enriched with the materials ispurified by means of cation exchange resin treatment, extraction with anaqueous acid solution or distillation followed by recycling for re-usefor the same purpose. Thus further reduction in the by-produetion of PNas well as further increase in the yield of ADN was facilitated.

The method of the present invention can be applied to any of theelectrolytes obtained by known electrolytic processes, as well as of theliquids obtained in the course of separation of ADN from theelectrolyte, for example,

3 liquids from separation of AN and PN from the electrolyte.

DESCRIPTION OF THE INVENTION As the electrode reaction-impairingmaterials are mentioned reduction products of nitriles and hydrolysisproducts of nitriles, cyanoethylated products of ammonia such as, forexample, B-aminopropionitrile and iminodipropionitrile and thehydrolysis products thereof, cyclization products of ADN such as, forexample, those described by O. E. Thompson in J. Amer. Chem. Soc. 80,5483 (1963) and hydrolysis products thereof, decomposition products ofquaternary ammonium salts and the like.

In carrying out the method of this invention, the electrolyte containingAN, ADN and an electrolytic supporting salt is continuously orintermittently drawn out as the electrolysis progresses and separatedinto oily and aqueous layers by the use of a method described in U.S.Pat. 3,267,131 wherein water and AN is added to a homogeneous solution,a method described in Belgian Pat. 706,573 wherein an emulsion istreated or of a oil separation device, for example, Coalescer (tradename) manufactured by Nippon Filter Industries Co., Ltd. The oily layercontains less water and electrolytic supporting salt and more ADN, AN,2-cyanoethyladiponitrile and PN, whereas the aqueous phase, contrary tothe oily layer, contains more electrolytic supporting salt and water.

It is preferable during the separation to maintain pH of the aqueousphase separated between 5 and 11 because of tendency for the basicelectrode reaction-impairing meatrials to be more transferable intoaqueous layer under acidic condition and into oily layer under thealkaline condition. At pH higher than 11, by-products such asbis-cyanoethyl ether will be formed with unfavorable results. Adjustmentof pH is preferably made by adding a hydroxide comprising the cation ofthe electrolytic supporting salt or an acid comprising the anion of thesame, but is not restricted by the above-mentioned. When theelectrolysis is carried out in an electrolyzer with a cathode chamberand an anode chamber divided by a cation exchange membrane, pH of theoutlet liquid of the electrolyzer is usually higher than that of theinlet liquid due to a small anion transportation of the cation exchangemembrane and naturally the concentration of electrode reaction-impairingmaterials is higher in the outlet liquid. In this respect, theelectrolyte to be subjected to purification is preferably the outletliquid of the electrolyzer.

As the means by which the electrode reaction-impairing materials areeliminated there is mentioned the treatment of the separated oily layerwith a cation exchange resin for removal by adsorption of the impairingmaterials. Although, the cation exchange resin may be either a stronglyacidic resin or a weakly acidic resin, those of H-form or the form ofthe cation of the salt of the electrolytically supporting salt ispreferable. In general, the lower the degree of crosslinkage of theresin (content of divinylbenzene contained in the resin), the superiorare both the rate of exchange and the capacity of adsorption, whereasthe inferior are the mechanical properties due to great physical changessuch as swelling and shrinkage. Accordingly, it is recommended that aporous resin or MR resin (macro reticular structure resin), for example,Amberlite- 200 manufactured by Rohm and Haas is used. The amount ofresin used isv from 0.3 to 2 ml./ampere-hour (abbreviated a-hr.hereinbelow) in terms of the acid form. Regeneration of the resin iseffected by conventional procedures.

Another means for eliminating the electrode reactionimpairing materialsis the extraction of the separated oily layer with an aqueous acidsolution. The aqueous acid solution may be of a strong acid, weak acidor acid salt and is preferably a solution having a pH of 5-1 of theanion forming the electrolytic supporting salt. The extraction is madeusing a packed column, sieve tray or the like and the amount of aqueousacid solution employed 4 is preferably from 0.05 to 5 times as much asthe oily layer. Recovery of ADN and AN is also conducted by extractionthereof with a by-product PN or another organic solvent. Another methodof purification of the oily layer, which is a more preferableembodiment, involves, while carrying out the purification of the oilylayer, add ing ADN to the aqueous layer separated to transfer theelectrode reaction-impairing materials into the ADN, then separating theADN layer and the aqueous layer, recycling the aqueous phase to thecatholyte and purifying the ADN layer by distillation for re-use for thesame purpose. Removal of the electrode reaction-impairing materials fromboth the oily and aqueous layers reduces the amount of theelectrode-reaction impairing materials in the catholyte to substantiallynegligible amount whereby the electrolysis under better conditionsbecomes feasible. Reduction of by-production of PN and increase in theyield of ADN can be thus achieved. In addition, in any of theabovementioned, addition of ADN purified by such a means as distillationprior to separation of the electrolyte into oily and aqueous layersenables removal of the electrode reaction-impairing materials in alarger amount from the aqueous layer, due to the fact that the electrodereaction-impairing materials are soluble in ADN and contact of a largeamount of oily layer with the aqueous phase enables the betterdistribution of the electrode reaction-impairing materials into the oilylayer. Addition of AN in place of the ADN will increase AN concentrationin the aqueous layer too much with the result that by-production ofZ-cyanoethyladiponitrile, bis-cyanoethyl ether, polyacrylonitrile andthe like will be increased to adversely affect the stable production ofADN in a high yield for a prolonged period of time. It is thereforeunfavorable for the desired transfer of the impairing materials in asatisfactory amount into the oily layer.

The oily layer with the electrode reaction-impairing materials removed,which is then recycled to the electrolyte, is preferably purified asfrequently as possible. In order to maintain the yield of ADN on thebasis of AN consumed over for a long period of time it is at leastnecessary to keep the alkali value below 30. It is accordinglypreferable to purify and recycle the oily layer continuously orintermittently at a rate from 0.5 to 50 mL/a-hr. At rates higher than 50mL/a-hr. economy will be a burden, though the yield of ADN can bemaintained high. Alkali value, as used herein, is the amount of alkaliin milliequivalent/l. required for raising pH from 5 to 11 of theelectrolyte following purge with nitrogen at pH 3 to remove carbondioxide subtracted by the value with a fresh electrolyte containing noelectrode reactionimpairing materials at an equal concentration, whichis taken as being quantitatively indicative of electrodereaction-impairing materials.

As the electrolyzer used for the hydroelectrolytic dimerization of ANthere may be used either an electrolyzer divided by a diaphragm into ananode chamber and a cathode chamber or one without diaphragm. The formeris preferred however. Either a neutral diaphragm or one selectivelypermeating cations may be used as the diaphragm. The latter ispreferable.

The cathode is made of a material with a high hydrogen overvoltage suchas mercury, lead, zinc or cadmium, preferably of lead or lead alloy.

The electrolyte is a homogeneous solution or an emulsion containing AN,ADN and by-products therewith, an electrolytic supporting salt andadditives effective for the electrolysis such as a polymerizationinhibitor and an emulsifier. As the electrolytic supporting salt aregenerally used electrolytic salts represented by the general formulawherein Ih-R, is alkyl containing from 1 to 4, preferably from 2 to 3carbon atoms and X is sulfate, alkylsulfate of the general formula RSwherein R is alkyl containing 1-4 carbon atoms or aryl sulfonate of thegeneral formula wherein R is alkyl containing 0-2 carbon atoms. Otheranions that may be used as effective for the hydrodimerization arehalogen, nitrate, phosphate and the like.

Although any anolyte may be used in the divided cell provided with adiaphragm, those which produce little adverse effects upon corrosionresistance of the anode and the electrolytic hydrodimerization and areinexpensive are preferable. Especially preferred is sulfuric acid. Theelectrolyte is passed through the electrolyzer at a flow rate from 1 to500 cm./sec., preferably from 10 to 200 cm./ sec. while maintaining thepH between 3 and 10. The temperature at which the electrolysis isconducted is preferably from 0 to 70 C. and the current density is 1-100a-/dm. preferably 5-30 a-/dm.

DESCRIPTION OF PREFERRED EMBODIMENTS This invention is described in moredetail with reference to flow sheets in the accompanying drawing.However, it is to be understood that the invention is not limited to theembodiments as indicated by the drawing. The flow sheet of FIG. 1 showsthe electrolyzer in which the electrolytic hydrodimerization is carriedout and the circulation system of the cathode and anode. In FIG. 1 theelectrolyzer 1 is composed of the cathode chamber 5 and the anodechamber 6 partitioned by the cation exchange diaphragm 7. The anolyte iscirculated between the anode chamber and the anolyte tank 3. Thecatholyte, which is a homogeneous solution or an emulsion containing AN,ADN, an electrolytic supporting salt and other additives, is circulatedbetween the cathode cell and the catholyte tank 2. Temperature of thecatholyte is controlled by the heat exchanger 4. FIG. 2 indicates therecovery step which involves separation of the catholyte into oily andaqueous layers, removal of PN and water and separation of ADN. In caseswhere the catholyte is an emulsion the catholyte is drawn from thecatholyte tank 2 and separated into oily and aqueous layers in theseparation column 8. The oily layer drawn out of the top of theseparation column is passed to the AN stripper 9 in which low-boilingsubstances such as AN, PN and water are removed and high-boilingsubstances mainly composed of ADN are drawn out through the nozzle 14.The oily layer drawn out from the nozzle 14, which is free fromlow-boiling substances is passed to the purification step. The aqueouslayer drawn out from the bottom of the separation column 8 is subjectedin the water stripper to removal of low-boiling substances mainlycomposed of water and then returned to the catholyte tank 2. Thelow-boiling substances distilled out in the AN stripper 9 and the waterstripper 10 are collected in the decanter 11 in which distillate mainlycomposed of AN and PN and one mainly composed of water are separated.The former distillate is passed from the top of the decanter 11 to thePN stripper 12 through which PN is separated from the bottom nozzle 15.The distillate mainly composed of water is passed from the bottom of thedecanter 11 to the water stripper 13, through which water is separatedfrom the bottom nozzle 16. The distillates obtained from the PN stripper12 and the water stripper 13 are recovered in the catholyte tank.Separation in cases where the catholyte is a homogeneous solution iscarried out by first admixing a mixture of the distillate mainlycomposed of AN and PN and one mainly composed of water at an appropriateproportion through the pipe with the catholyte prior to entering intothe separation column to a heterogeneous solution, which is subsequentlyseparated into oily and aqueous layers. The nozzle 17 is employed forsupplying AN in accordance with the decrease of AN due to the conversionto ADN. Addition of ADN, if required, is made through the nozzle 20 inthe same way as with separation of the homogeneous solution. FIGS. 3 and4 show the purification step for carrying out the method of the presentinvention. Referring to the flow sheet on FIG. 3, which shows teratmentof the oily layer with a cation exchange resin following separation ofthe catholyte into oily and aqueous layers, the catholyte drawn out ofthe catholyte tank 2 is mixed with an acid or alkali introduced throughthe nozzle 26, pH being adjusted to a predetermined value and thenpassed to the separation column *8. The aqueous layer thus separated isneutralized with an alkali or acid introduced from the bottom of theseparation column 8 through the nozzle 27 to pH of the catholyte andsubsequently passed through 21 to the water stripper 10. The oily layeris drawn out from the top of the separation column 8, a part of which isled to the AN stripper 9 (not shown) and the rest is sent to cationexchange column 18 where the material is removed by the adsorption. Theresultant efiluent is then recycled to the catholyte tank 2. As occasiondemands during the treatment the cation exchange resin is regeneratedwith a regenerating solution stored in the tank 19 and then washed withpure water introduced through the nozzle 21. The cation exchange column,which is operated batchwise according to the drawing, may be operated ina continuous manner. The nozzle 25 is an outlet for the outflow duringregeneration.

Referring to the flow sheet on FIG, 4, which shows countercurrentextraction of the acid phase after separation of the catholyte into oilyand aqueous phases, using an aqueous acid solution, the pH of thecatholyte drawn out from the catholyte tank 2 is adjusted to apredetermined value by adding an acid or alkali introduced through thenozzle 26 and the treated catholyte is passed to the separation column"8. The aqueous phase separated is neutralized with an alkali or acidintroduced through the nozzle 27 to a pH of the catholyte and passedthrough 21 to the AN stripper 9 (not shown). The rest of the oily phaseis passed to the extraction column 28 through the bottom thereof filledwith Raschig rings and extracted with an aqueous acid solution in acountercurrent manner therein. The oily phase withdrawn from theextraction column 28 is passed to the catholyte tank 2. The aqueous acidsolution withdrawn from the extraction column 28 is drawn out throughthe nozzle 31 and treated with an appropriate organic solvent such asPN, methylene chloride or benzene to recover ADN and AN.

Example 1 An electrolyzer having a cathode chamber and an anode chambereach 10 cm. x 10 cm. x 1 mm. in size, equipped with a cathode of leadalloy containing 6% antimony and an anode of lead alloy containing 0.7%silver and 6% antimony, each having an effective area of electrodesurface of 10 cm. x 10 cm., partitioned by a cation exchange diaphragm 1mm. in thickness was used. Using an experimental apparatus as shown inFIGS. 1-3, 2 N aqueous sulfuric acid as an anolyte was circulated at aflow rate of 200 ml./sec. and as a catholyte an emulsion consisting of a8:2 by volume mixture of anaqueous layer consisting of 2% AN, 6% ADN,8.0% tetraethylammonium sulfate, 0.05% emulsifier and the balance ofwater and an oily layer containing 17% AN, 75% ADN, 5% water and 3%by-products mainly composed of 2-cyanoethyladiponitrile and PN, pH beingadjusted to 8, was circulated at a flow rate of 200 ml./ sec. Theelectrolysis was carried out at a liquid temperature of 50 C. at anelectric current density of 10 a./dm. The catholyte effluent was passedto the separation column 8 where it is separated by means of a settlingseparator (not shown) into an aqueous layer and an oily layer, thelatter being sent to the AN stripper 9 and the rest of the oily layercontinuously passed through a cation exchange resin column at a flowrate of 200 m1./hr. and then returned to the catholyte tank 2. As

Alkali ADN PN value 100 hours 92 5. 6. 0 1,000 hours 90 7. 0 8. 3

The results were quite satisfactory in view of the fact that the surfaceof the cathode on completion of the electrolysis had agglutinatesadhered in amount less than as much as those observed in theelectrolysis without the above-mentioned treatment.

Comparative Example 1 The electrolysis was carried out in the same wayas in Example 1 except that no treatment with the cation exchange resinwas applied. The results are shown below.

Alkali ADN PN value 250 hours 91 6. 0 7. 2 1,000 hours 75 20. 3 37. 2

The operation was terminated after 1160 hours because of muchagglutinates adhering upon the surface of the cathode.

Example 2 An electrolysis was carried out on, as catholyte, ahomogeneous solution containing 12% AN, ADN, 35% tetraethylammoniump-toluenesulfonate and the balance of water. A portion of the catholytewas mixed with AN, PN and water recovered from the decanter 11 to aheterogeneous solution, which was treated with tetraethylammoniumhydroxide to adjust pH of the aqueous phase to 9. Then the resultantmixture was allowed to stand in the separation column 8 for separation.The aqueous layer separated was neutralized with p-toluenesulfonic acidand passed to the water stripper 10. The oily layer was passed to the ANstripper 9 and the balance was continuously passed through a cationexchange column and then re turned to the catholyte tank 2.

As the cation exchange resin there was used l. of Dowex 50WX4 in acidform manufactured by Dow Chemical. A 1500 hours continuous operation wascarried out in the same experimental conditions as in Example 1 exceptfor the above. The yields of ADN and PN on the basis of theAN consumedwere as follows:

ADN PN 300 hours 90 7. 0 1,500 hours".-. 88 9. 4

At the end of the operation, the amount of agglutinates which adhered onthe surface of the cathode was observed to be slightly more than thosein Example 2.

Comparative Example 2 ADN PN 1st run"... 400 hours 90 7. 5 2d run. 800hours. 86 8. 7 3d run- 78 14. 3 4th run 71 19. 1

Following the third run, further 400 hours continuous operation ofelectrolysis was unfeasible due to the polymeric material agglutinatedupon the surface of the electrode. The table indicates that the yield ofADN decreased due to the material accumulated in the catholyte even withthe cleaning of the surface of the electrode.

Example 3 Referring to FIG. 4, the extraction column 28 was filled withRaschig rings and the separation column 8 was an oil-separation tube(Coalescer) A portion of the catholyte was separated into an aqueouslayer and an oily layer with pH of the aqueous layer adjusted to 10 withtetraethylammonium hydroxide. Thus separated aqueous layer wasneutralized with an aqueous sulfuric acid and then passed to the waterstripper 10 while the oily layer was passed through the AN stripper 9 tothe extraction column. To the top of the extraction column 28 wassupplied the aqueous sufuric acid of pH=2, and from the bottom wassupplied the oily layer in the ratio of 5:1, the countercurrentextraction taking place between them. A portion of the treated oilylayer was then passed to the purification step and the balance to thecatholyte tank 2. The aqueous sulfuric acid solution enriched withelectrode reaction-impairing materials was in turn extracted with PN andthe layer containing AN, PN and ADN was sent to the AN stripper. Resultsof a 1500 hours, continuous operation under the same conditions as inExample 1 except for the above are shown below with reference to theyields of ADN and PN on the basis of the AN consumed,

ADN PN 150 hours 91 6. 0 1,500 hours 89 7. 8

The condition of the surface of the cathode on completion of theelectrolysis was similar to that as observed in Example 1.

Example 4 The whole process was run according to the flow sheet shown inFIG. 2 except that a portion of the catholyte was not passed to theseparation column but directly sent to the water stripper 10, in whichlow-boiling substances such as AN, PN and water were distilled out. Tothe resulting liquid, after being cooled, was added ADN at a rate of 100ml./hr. Then to the resulting mixture was added tetraethylammoniumhydroxide to adjust pH of the aqueous phase obtained after separation to10, and the whole was mixed. The resulting mixture was allowed to standin the separation column 8 for settling and the separated oily layer waspassed through a cation exchange column at a rate of 250 ml./hr. forpurification, treated effluent being recycled for re-use. The separatedaqueous layer was neutralized with sulfuric acid and then passed to thecatholyte tank 2. Results of a 1500 hours continuous operation under thesame experimental conditions as in Example 1 except for the above areshown below with reference to the yields of ADN and PN on the basis ofthe AN consumed.

ADN PN 400 hours 90 7. 3 1,500hours- 87 9. 1

Upon completion, the agglutinates which adhered to the surface of thecathode was less than those observed in Example 1.

Example 5 The example shows an electrolysis accompanied by the additionof ADN to the catholyte efiiuent and cation exchange of the oily layerseparated from it. A portion of the catholyte, prior to entering intothe separation column 8, was subjected to addition of ADN at a rate ofl00 ml./hr. and tetraethylammonium hydroxide and subsequently toseparation into oily and aqueous layers by the use of an oil-separationtube (Coalescer). The aqueous layer separated, pH 10, was neutralizedwith sulfuric acid and then passed to the water stripper 10. A portionof the oily layer was passed to the AN stripper 9 while the rest waspassed through the cation exchange column 18, giving purified liquid,which was then recycled to the catholyte tank. Thus, the alkali value inthe catholyte was maintained below 10. As the cation exchange resinthere were used 3.0 l. of Amberlite IRC-84 of tetraethylammonium form.Results of a 1500 hours continuous operation under the same experimentalconditions as in Example l are shown below with reference to the yieldsof ADN and PN on the basis of the AN consumed.

ADN PN 200 hours 92 4. 9 1,500 hours--." 90 6.

The agglutinates on the surface of the cathode on completion of theelectrolysis were less than those in Example 1.

Example 6 The example shows an electrolysis on a catholyte containing adifferent electrolytic supporting salt, in an undiaphragmedelectrolyzer, while adding ADN to the electrolyte effluent andextracting the oily layer. As the electrolyte there was used an emulsionprepared at pH 7 from an 8:2 by volume mixture of an aqueous layerconsisting of 1% tetraethylammonium acid phosphate, 20% sodium acidphosphate, 2% AN, 2% ADN, 4% ADN, 0.05% emulsifier and the balance ofwater and an oily layer consisting of 17% AN, 75% ADN, 5% water and 3%byproducts mainly composed of 2-cyanoethyladiponitrile and PN. Thecatholyte tank 2 as shown on the flow sheet of FIG. 1 was used alone. Aportion of the electrolyte was not passed to the separation column 8 butdirectly to the water stripper 10 in which low-boiling substances suchas AN, PN and water was distilled olT. The residual liquid was thencooled, to which were added A-DN at 100 ml./ hr. and sodium hydroxide.The mixture was allowed to stand in the separation column 8 forseparation. The aqueous phase separated, pH 10, was neutralized withphosphoric acid prior to returning to the catholyte tank 2. A portion ofthe oil phase was passed to the purification step and the balance to theextraction column 28 filled with 'Raschig rings. Thus, alkali value ofthe electrolyte in the electrolyzer was maintained below 20. In theextraction column 28, countercurrent extraction was made between theaqueous phosphoric acid solution of pH=2.S and the oily layer at theratio by volume of 1:5. The resulting oily layer was passed to thecatolyte tank 2 while the aqueous phosphoric acid was contacted with PNfor recovery of ADN therefrom, and then discarded. Results of a 360hours continuous operation conducted under the same experimentalconditions as in Example 1 except for the above and those without theabove-mentioned treatment were compared with reference to the yields ofADN and PN on the basis of the AN consumed.

With Without treatment treatment ADN PN ADN PN 50 hours 78 75 15 360hours 75 17 58 35 The agglutinates on the surface of the cathode oncompletion of the electrolysis amounted to less than as much as thoseproduced in the electrolysis without the treatment.

Example 7 10 below. The electtrolysis without treatment could beoperated at longest for 300 hours due to much hydrogen gas evolved bythe agglutinates on the surface of the cathode.

With Without treatment treatment ADN PN ADN PN 50 hours 70 26 68 28 300hours 70 27 38 58 The surface of the cathode on completion of theelectrolysis had agglutinates adhered in amount about as much as thatobtained when the electrolysis was carried out without the abovetreatment.

Example 8 An electrolysis was conducted as in Example 1 in which theaqueous layer separated was placed in a separate tank and mixed with ADNadded at a rate of 200 ml./hr. The mixture was then passed to aseparation column separately set up. The ADN phase was purified in thepurification step by distillation for use in recycling. The aqueousphase was passed to the water stripper 10. Results are shown below.

ADN PN 500 hours 91 6. 9 1,500 hours"... 92 6.1

The amount of agglutinates on the surface of the cathode on completionof the electrolysis was about /5 as much as that in Example 1.

Example 9 ADN PN 450 hours 92 6. 0 1,500 hours. 91 6. 5

The amount of agglutinates on the surface of the electrode on completionof the electrolysis was about A as much as that in Example 3.

We claim:

1. In the process for electrolytically hydrodimerizing acrylonitrile,improvement which comprises separating an electrolyte efiiuentcontaining an electrolytic supporting salt, acrylonitrile, adiponitrileand electrode reaction-impairing materials into oily and aqueous layers,removing the electrode reaction-impairing materials contained in theoily layer and recycling the resulting oily layer thus purified to theelectrolyte.

2. Method according to claim 1 wherein a homogeneous aqueous solution isused as the electrolyte.

3. Method according to claim 1 wherein an emulsion is used as theelectrolyte.

4. Method according to claim 1 wherein adiponitrile is added to saidelectrolyte to effect separation thereof into oily and aqueous layers.

5. Method according to claim 4 wherein additional adiponitrile is addedto said separated aqueous layer to transfer electrode reaction-impairingmaterials contained in said aqueous phase into an adiponitrile phase andthe adiponitrile layer thus containing the electrode reactionimpairingmaterials is purified by distillation.

6. Method according to claim 1 wherein pH of the separated aqueous layeris from 5 to 7.

7. Method according to claim 1 wherein said separated oily layer iscontacted with a cation exchange resin thereby adsorbing thereon saidelectrode reaction-impairing materials.

8. Method according to claim 1 wherein said separated oily layer iscontacted with an aqueous acid solution thereby transferring electrodereaction-impairing materials into the aqueous acid solution for removalof the same.

9. Method according to claim 1 wherein rate of said only phase treatedis from 0.5 ml. to 50 mL/a-hr.

10. Method according to claim 7 wherein said cation exchange resin is ofH-form or the form of cation of the electrolytic supporting salt.

11. Method according to claim 7 wherein rate of the cation exchangeresin used is from 0.003 to 2 rnl./a-hr.

12. Method according to claim 8 wherein pH of said aqueous acid solutionis from 5 to 1.

13. Method according to claim 8 wherein amount of the aqueous acidsolution for the extraction is from 0.5 to 50 times as much as that ofthe oily layer to be treated.

References Cited UNITED STATES PATENTS 3,267,131 8/1966 Campbell et a1260-46S.8 3,402,112 9/1968 Brubaker et al. 204-73 A 3,484,348 12/ 1969Johnson et al. 204--73 A 3,493,597 2/ 1970 Campbell et a1. 204--73 A3,497,429 2/ 1970 Mihara et al 204-73 A 3,595,764 7/1971 Seko et al204--73 A J. C. EDMUNDSON, Primary Examiner US. Cl. X.R. 204-237

